1. Field of the Invention
The present invention relates to a press fabric for use on the press section of a paper machine. Specifically, it relates to a press fabric, including several embodiments thereof, which is manufactured according to the techniques used to weave forming fabrics, and which has an extremely fine surface formed predominantly by fine monofilament or multicomponent yarns.
2. Description of the Prior Art
The press section of a paper machine generally includes at least one press designed to remove water from a fibrous web, which is a nascent paper sheet. Each such press includes a press nip, which is a region of elevated compression to squeeze water from the fibrous web. The press nip itself may be formed between two adjacent press rolls. Alternatively, according to a more modern press design, the press nip may be formed between a press roll and an arcuate pressure shoe having a cylindrically concave surface of radius substantially equal to that of the press roll. A press nip formed in this manner is several times longer, in a machine, or longitudinal, direction than one formed between two press rolls. Such is the origin of the terminology commonly used by those skilled in the art to refer to this variety of press--the extended nip press.
Those in the papermaking industry are continually seeking ways to provide a quality paper product more efficiently and economically. In particular, paper manufacturers are continually striving to reduce the energy costs which accompany paper production. These costs arise because steam is normally provided to heat, from within, the series of rotatable dryer cylinders which make up the dryer section, a final stage in a paper machine. It is in the dryer section that the water remaining in the fibrous web, upon its exit from the press section, is removed by evaporation by passing the web around each in a series of dryer cylinders. The less water that remains in the fibrous web leaving the press section, the less water will have to be removed by evaporation in the dryer section, and, as a consequence, the lower will be the costs associated with the production of steam for that section.
The present invention is directed to this need to remove more water from the fibrous web in the press section, thereby leaving less to be removed in the dryer section. As previously noted, water is removed from the fibrous web in the press section by passing the web through at least one press nip. More particularly, the fibrous web passes through the nip in conjunction with at least one press fabric, which supports it in its still fragile condition, and which accepts the water squeezed therefrom in the nip. Commonly, the fibrous web passes through the press nip sandwiched between two such press fabrics.
It is a goal, then, of the present invention, to bring about an increase in the amount of water removed from the fibrous web in the press section by increasing the water-handling ability of the press fabrics used thereon. It is a further goal to increase the water-handling ability of the press fabrics to such a degree that the speed of the paper machine may be increased without sacrificing the structural integrity or degree of dryness of the fibrous web leaving the press section en route to the dryer section.